#13,453
Six years after its discovery, our understanding of how MERS-CoV transmits from zoonotic sources (camels) to humans - and onward from human-to-human - remains limited. While the same could be said for a number of other pathogens (see WHO List Of Blueprint Priority Diseases), the timely release of information on MERS has been particularly inconsistent and vague.
Camel contact - either direct or indirect - is almost certainly responsible for a large number of `primary' MERS cases, but exactly how - and under what conditions - this is most likely to occur remains poorly defined.Part of the problem has been cultural, since camels are a much beloved part of Saudi society, and as such were considered by many (including the MOA) to be incapable of spreading a disease like MERS (see Saudi Camel Owners Threaten Over MERS `Slander’).
Another problem has been political, with a veritable `revolving door' at the top of the Ministry of Health since 2013 (see Another Political Shake Up In Saudi Arabia), apparently due to frustrations over not making MERS go away.
The result has been fragmented data on the virus - particularly prior to 2015 - but which remains a problem today (see The Saudi MOH Breaks Their Silence On MERS-CoV), which undoubtedly hampers the ability of researchers to understand the virus.Attempting to piece together the puzzle pieces, we've a new study published yesterday in the Journal Viruses, which looks at cases reported to the WHO (WHO) between 1 January 2015 and 13 April 2018, in order to parse out the influence of `direct' and `indirect' camel contact on the spread of the disease.
Note: Information on cases reported prior to January 1st, 2015 was deemed too inconsistent to be used in this analysis.Those hoping for a definitive resolution, however - like that unveiled on the last page of an Agatha Christie novel - will be disappointed. There remain significant gaps in both the data, and our understanding of this emerging pathogen.
The full open-access study is available at the link below - I've only posted some excerpts from a much longer study.
Viruses 2018, 10(8), 425; doi:10.3390/v10080425Article
Reported Direct and Indirect Contact with Dromedary Camels among Laboratory-Confirmed MERS-CoV Cases
Romy Conzade 1,2,†, Rebecca Grant 1,3,†, Mamunur Rahman Malik 4, Amgad Elkholy 4, Mohamed Elhakim 4, Dalia Samhouri 5, Peter K. Ben Embarek 6 and Maria D. Van Kerkhove 1,*
Abstract
Dromedary camels (Camelus dromedarius) are now known to be the vertebrate animal reservoir that intermittently transmits the Middle East respiratory syndrome coronavirus (MERS-CoV) to humans.
Yet, details as to the specific mechanism(s) of zoonotic transmission from dromedaries to humans remain unclear. The aim of this study was to describe direct and indirect contact with dromedaries among all cases, and then separately for primary, non-primary, and unclassified cases of laboratory-confirmed MERS-CoV reported to the World Health Organization (WHO) between 1 January 2015 and 13 April 2018.
We present any reported dromedary contact: direct, indirect, and type of indirect contact. Of all 1125 laboratory-confirmed MERS-CoV cases reported to WHO during the time period, there were 348 (30.9%) primary cases, 455 (40.4%) non-primary cases, and 322 (28.6%) unclassified cases. Among primary cases, 191 (54.9%) reported contact with dromedaries: 164 (47.1%) reported direct contact, 155 (44.5%) reported indirect contact. Five (1.1%) non-primary cases also reported contact with dromedaries. Overall, unpasteurized milk was the most frequent type of dromedary product consumed.
Among cases for whom exposure was systematically collected and reported to WHO, contact with dromedaries or dromedary products has played an important role in zoonotic transmission.
(SNIP)
MERS-CoV appears to be transmitted inefficiently between humans through casual contact in the general community [3]. In contrast, limited human-to-human transmission has occurred in healthcare settings from unprotected contact with or inadequate infection prevention and control measures in the care of MERS patients [4,5,6,7,8,9,10].
(SNIP)
Details as to the specific mechanism(s) of zoonotic transmission from dromedaries to humans remain unclear. Routes of camel-to-human MERS-CoV transmission likely include direct exposure to infected dromedaries and/or from an indirect exposure, including droplets of respiratory secretions from infected animals, or possibly through consumption of unprocessed and contaminated animal products, such as urine, unpasteurized milk, or raw meat [39].
Detailed epidemiological data on non-human exposures, such as direct or indirect animal exposure, have thus far been limited to a few case-control studies [40]. Studying MERS-CoV at the animal-human interface, and the routes of zoonotic transmission, highlights the need for a One Health approach to this research [41].
(Continue. . . )
What these researchers found was of the 1125 cases examined, just under 1/3rd (n=348) were classified as `primary' cases (no known exposure to a suspected or confirmed MERS case). Of those, just over half (54.9%) reported either direct, or indirect exposure (or both) to camels.
Those with camel exposure were overwhelmingly male (71.8%), generally older (mean age was 54.9), and 90% were from Saudi Arabia. For all cases reporting indirect contact with dromedaries, unpasteurized camel milk was the most frequent type of camel product consumed.The authors write:
Although it is clear that contact with infected dromedaries are the primary source of recurrent introduction of MERS-CoV into the human population, mitigating spillover from dromedaries to humans has been limited by a lack of clarity on the modes of transmission between dromedaries and humans, the extent of spillover to humans, and the epidemiology of MERS-CoV circulation in dromedaries in large parts of Africa and South Asia.We've recently looked at the mysterious lack of MERS infections reported from Sub-Saharan Africa, despite the presence of MERS positive camels (see Eurosurveillance: Lack of Serological Evidence of MERS-CoV In Camel Abattoir Workers - Nigeria 2016).
While the authors of this study cite the improvements in data collection since early 2015, they also note that some gaps remain.
Even among data reported since 2015, there is some missing data for contact with dromedaries and there is a complete absence of information on the use of personal protective equipment (PPE; e.g., gloves, boots, coveralls, masks/respirators) when in direct contact with dromedaries, and on hygiene practices following contact with dromedaries. This limits our ability to draw conclusions from our dataset, as to how each case was infected and the exact route(s) of transmission.And:
Our dataset is also limited by our ability in classifying cases based on available information reported to WHO at the time of reporting by the country. For example, thorough outbreak investigations, which include full genome sequencing of the virus, may find that cases which were initially classified as non-primary cases, may in fact be primary cases, and this information was not regularly relayed to WHO. More complete case reporting, including exposures prior to symptom onset, would improve our ability to assess non-human exposures that may have led to primary MERS illness in humans.The authors summarize their findings:
Conclusions
In conclusion, a lack of systematic reporting on exposures and risk factors, including contact with dromedaries for each MERS case identified since 2012, prevents a clear understanding of how infection occurred in each case.
However, it is clear from the data reported that contact with dromedaries has played an important role in transmission of MERS-CoV into the human population from the dromedary reservoir.
In other words, six years in, we've a lot left to learn about MERS-CoV.As a result, further understanding the geographic scope of MERS-CoV circulation in dromedaries, and limiting direct and indirect contact with infected dromedaries, remains important for reducing zoonotic transmission of MERS-CoV.
